Anchoring system for fating drilling vessel

ABSTRACT

A system for anchoring a floating drilling ship. When a storm comes, the stern anchor lines are slackened, the ship is disconnected from the wallhead and permitted to rotate about its bow. Each stern anchor line is composed of two parts. The first part is sufficiently large to effect anchoring under normal conditions, and a second part of the anchor line is of a much smaller size and is connected to the larger part. The second part or having part is used for retrieving the larger part when the ship is repositioned over the well bore. A special two-step windlass wheel is provided to accommodate the two different size anchor chains.

United States Patent [72] lnventor Don H. Flickinger 2,732,178 [/1956 Chaney 254/167X c/o Pan American Trinidad Oil Company FOREIGN PATENTS P.O. Box 714 Trinidad [21 pp NO 88585 5,311 12/188] Great Britain 254/167 [22] Filed Apr. 23,1969 OTHER REFERENCES [45] Patented June 8,1971 R. D. OGG et al, Anchors and Anchoring; 1956, p. IO -ll Primary Examiner-Milton Buchler Assistant ExaminerF. K. Yee ANCHORING SYSTEM FOR FLOATING DRILLING Attorneys-Paul F. Hawley and John D. Gassett VESSEL 7 Claims, 5 Drawing Figs. 52 Us Cl ABSTRACT: A system for anchoring a floating drilling ship. 114/206, when a Storm comes, the stem anchor lines are Slackened, the 51 in Cl 1 254/ l ship is disconnected from the wallhead and permitted to rotate [so] l ti B63b 21/24 about its Each Stem anchor line is composed of two 1 l8 0 I 114/206, parts. The first p is sumciently large to efiect anchoring l7 5 5 175 g. 2% under normal conditions, and a second part of the anchor line 29 l is of a much smaller size and is connected to the larger part. 56 if 1 4 2, 84, l75/6.8, -54/1 The second part or having part is used for retrieving the larger l e creams CIM part when the ship is repositioned over the well bore. A special UNITED STATES PATENTS two-step Windlass wheel is provided to accommodate the two 2,653,796 9/1953 McGee et al. l 14/.5X different size anchor chains.

28 10A 34A 36A X 36D 34D -10 32 34H 36H 36E /34E d34G 34F PATENT ED Jun 819?! sum 8 BF 2 ANCHORING SYSTEM FOR FLOATING DRILLING VESSEL BACKGROUND OF THE INVENTION This invention relates to anchoring a drilling ship over a subsea well location. It relates especially to the use of an anchor chain having one part much larger than the other part and to a windlass wheel having stepped sprockets to accommodate each size anchor chain.

SETTING OF THE INVENTION The need for oil and gas has caused men to explore watercovered areas which may be productive of oil and gas. Some of these wells are drilled from fixed platforms. A fixed platform is merely a drilling deck platform supported above the water by piles extending down into the water bottom. In deep water this is not economical and it also becomes very difficult. Therefore, many wells in water-covered areas are drilled from floating drilling vessels. One type drilling vessel is the so-called dn'll ship" type; the shape of the ship is the conventional shape, that is, its length is many times its width. In this ship the drilling derrick is mounted over a vertical passage in the ship which is located ordinarily about midship. A riser pipe, which is a large diameter pipe, e.g., inches in diameter, extends from the drilling vessel to the subsea well. Drilling operations are conducted through this riser pipe.

The most frequently used method of anchoring a floating drilling vessel is to provide anchor lines from the bow and the stern of the ship to anchors on the bottom of the sea. By applying the correct tension to these anchor lines, it is possible in normal weather to maintain the ship in a reasonably fixed position. However, in severe storms it is nearly impossible to maintain anchor chains and anchors of sufficient strength to withstand the forces developed. This is particularly true of the ship is not headed into the storm, that is, if the wave and wind forces hit the ship broadside. It is well known that if the ship is permitted to head into the storm, the forces received by the ship are much less.

Heading an anchored ship into a storm is not simple. This is especially true in drilling ships where anchor lines are connected to both the bow and the stern. In the past, when a severe storm was forecast, the drill pipe and riser were pulled or otherwise secured and the swing-away" technique employed. In this technique the stern anchors are slackened, or if necessary, severed from the ship, and the ship swung around and headed into the stem. The anchoring is accomplished by the bow anchors. The ships propellers and rudders can be used to assist in swinging it into and maintaining the ship in its modified anchored position.

Ordinarily, when using the swing-away technique, there is not sufficient length of stem anchor chain to permit the ship to swing about the bow and maintain'the connection to the ship of the stern anchor lines. What normally happens in such situations is that the stern anchor lines are severed. The severed stern anchor lines are normally dropped to the ocean floor; however, before they are dropped, the end of the anchor chain is usually connected to a buoy so that the chain can be recovered. This recovery is quite time consuming and therefore costly. Before the drilling ship can be used to resume drilling, the stern anchor lines must be reconnected. In some areas the storms are so frequent that before or by the time the stern anchor chains have been reconnected, another storm occurs. Thus, little time is left or available for drilling. l have provided an improvement in the swing-away technique so that there is much more time left for drilling.

BRIEF DESCRIPTION OF THE INVENTION This invention relates to the anchoring of a drill ship in which the length is many times the width. Anchoring of this drill ship is normally obtained by bow anchors and stem anchors. The stem anchor lines are each of two parts. A first part is connected to the anchor and to the ship. It is of sufficient size and length to anchor the stern of the ship duringnormal drilling operations. The second portion of the anchor line is of a much smaller size and is not of sufficient strength to provide normal anchoring. A special windlass wheel is pro- 'vided which can accommodate either the large or the small section of the anchor line. The anchor line, including the large first portion and the small second portion, are fed through the same windlass wheel. The total length of the first and second portions of the anchor chain is sufficient to permit the ship to be swung around the bow through a total are of at least 200 without having to sever the stern anchor lines. When the ship is so rotated, the stern anchor lines provide no anchoring for the vessel. The additional small length of anchor chain is sufficiently strong to retrieve the heavier anchoring portion of the anchor chain.

DESCRIPTION OF THE DRAWINGS Various objects and a better understanding of the invention can be had when taken in conjunction with the following description and the drawings.

FIG. 1 illustrates an anchored floating vessel;

FIG. 2 illustrates a plari view of a drill ship and anchor array for explaining the swing-away technique;

FIG. 3 illustrates the connecting link between the large anchoring chain and the smaller heaving chain;

FIG. 4 illustrates a cross section perpendicular to the axis of my two-step sprocket windlass wheel;

FIG. 5 illustrates another section view of a windlass wheel taken along line 5-5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a drill ship 10 floating on a body of water 12. It is anchored to an anchor 14 in the floor 16 of the body of water by an anchor line. This anchor line is of two portions. The first portion is a heavy anchoring chain 18 which extends from anchor 14 through windlass 20 and anchor stop 22. Anchor chain 18 is connected to a smaller or heaving portion 24 which is in the anchor chain locker 26. Typically, the anchoring chain 18 can be a 3-inch anchor chain. Typically, the heaving portion 24 can be a l-inch chain.

Attention is next directed to FIG. 2 which illustrates the swing-away technique. Shown thereon is drilling vessel 10 with a bow 28 and a stem 30. A drilling rig 32 is placed over a vertical well through the midsection of the ship 10. Normally, a riser pipe, not shown, extends from this down through the subsea wellhead in a well-known manner.

In FIG. 2, ship 10 is anchored to anchors 34A, 34B, 34C, 34D, 34E, 34F, 34G and 34H by anchor lines 36A to 36H. Anchor lines 36A, 36B, 36C and 36D are called bow lines and anchor lines 36E, 36F, 366 and 36H are called stern anchor lines. It is a modification of the stern anchor lines and their associated windlass which is the main feature of my invention which makes the swing-away technique practicable.

When drilling vessel 10 is first anchored, it is headed into what is believed to be the prevailing direction of wind and waves. However, during a storm the direction of the wind and waves can change. Frequently, it is desired to rotate the ship about the bow 28 in order to head the ship into the storm. As mentioned above, before this is done, the riser pipe is disconnected from the wellhead. If time permits, the riser pipe can be pulled onto the vessel. Then the ship is swung around to a new position such as illustrated by dotted line 10A. It will be noted that the ship has pivoted in a are about the bow. Before this rotation can be accomplished, the stern anchor lines 36E, F, G and H have to be slackened or severed. In my invention the lines are not severed but are merely slackened. A typical length of drill ship 10 is about 700 feet. In normal operations in 300-400 feet of water, for example, for a drill ship of this size, approximately 2,500 feet of chain is adequate for anchoring the vessel. Thus, for example, chains 36E through H can have a first part of about 2,500 feet long of 3-inch chain. When it is desired to rotate vessel 10 about its bow, additional stern anchorage chain is necessary if severing of the anchoring chain is to be avoided. Typically, this can be about 1,000 feet. This additional 1,000 feet, I call heaving chain. This heaving chain is not of sufficient strength to effect anchoring of the vessel. However, it is sufficiently strong to be used for retrieving the heavier anchoring section which may be 3-inch chain, for example. Thus by using the lighter heaving chain, the heavier anchoring chain can be quickly retrieved when the storm subsides. Then drilling operations can be recommenced within a very short period of time such as 4 to 6 hours, for example, whereas without my invention it has taken days to reanchor the ship.

Attention is next directed to FIGS. 4 and which illustrate a novel windlass wheel which can accommodate both the large anchoring chain and the smaller heaving chain. It is essential that one windlass wheel can accommodate both the heaving chain and the anchoring chain as both are stored in the same chain locker and utilize the same hawse pipe. Attention is first directed to FIG. 5 taken along the line 5-5 of FIG. 4 and which shows a windlass wheel 40 driven about its axle 42 by a power source, not shown. The windlass wheel 40 has a first sprocket system of large size for the anchoring section of the chain and a smaller sprocket system for the heaving portion of the chain. A part of the larger sprocket system is a circumferential-like groove 44 which has a sufficient width 45 to accommodate the width of the larger chain. A second circumferential groove 46 is provided and has a lesser width than groove 44 so that shoulders 45A and 45B are formed in the bottom of groove 44. Teeth or sprockets 54, as can be seen more clearly in FIG. 4, are mounted on these shoulders 45A and 458. A third circumferential groove 48 having a smaller width than groove 46 is also provided. Thus, shoulders 47A and 47B are formed. Sprockets 52 are mounted on these shoulders.

FIG. 4 illustrates a cross-sectional view of the windlass wheel 50 taken perpendicular to the axis thereof. It shows a series of sockets 52 about groove 48. These are for the small chain. FIG. 4 also shows a series of teeth 54 which are placed about the circumferential-like groove 44 for the larger chain.

Grooves 44, 46 and 48, shown in FIG. 5, can be called concentric grooves. Grooves 44 and 46 are sized to accommodate the larger anchoring chain and grooves 46 and 48 are sized to accommodate the smaller heaving chain. As an example, for a 3-inch anchoring chain, typical dimensions of the width 45 and the radial depth 47 of groove 44 are 12 inches and 6 to 8 inches, respectively. Typical dimensions for groove 46 for such chain include a width of about 4 to 6 inches and a radial depth of 4 to 6 inches; and for groove 48 include a width of about I yg inches and a radial depth of about 2 inches. Typically, the overall diameter of the windlass wheel of FIG. 4 for the 3-inch anchoring chain and 1-inch heaving chain can be about 4 or 5 feet.

FIG. 3 shows a pear-shaped connecting link 60 which connects the smaller heaving chain 24 to the larger anchoring chain 18. In operations, both parts of these chains are threaded through the windlass described above and illustrated in FIGS. 4 and 5.

While the above embodiments have been described with a great deal of detail, it is possible to produce modifications thereof without departing from the spirit or scope of the invention.

I claim: 1. A method of mooring a ship floating on a body of water which comprises:

providing a stern anchor line of two parts, a first part being of sufficient size and length to anchor said ship to a subsea anchor and a second part of a size smaller than said first part;

anchoring the stern of said ship with said first part of said line;

anchoring the bow of said ship;

releasing the stern anchor line by lowering the first part into the water by paying out said second part sufficiently so that said stern anchor line is not effective to anchor the chi r i gihg the ship position as required so that it is headed into a storm;

after the storm has subsided taking in on the second part of said stern anchor line to retrieve said first part; reanchoring the stern of said ship with said first part of said stern anchor line.

2. In the method of claim 1 in which said ship is a drilling ship which includes the steps of:

placing a riser pipe into the water so as to connect a subsea well with the ship, including connecting the upper end of said riser pipe to said ship;

releasing said riser pipe from said well prior to releasing said stern anchor line.

3. A method as defined in claim 2 including the step of swinging the ship about its bow so that it heads into a storm by operating the ships propulsion system and taking up on at least one bow anchor line.

4. A method as defined in claim 2 in which said anchor line is a chain having an anchoring section connected to a heaving section and including the step of threading said stern anchor chain over a double sprocket system windlass having a first sprocket system being of a size to accommodate said anchoring portion, and said second sprocket system being of a size to accommodate said heaving portion;

operating said windlass to take up or let out said stern anchor chain.

5. An anchoring system for a ship floating on a body of water which comprises:

an anchor;

a windlass wheel for use with an anchor chain having a first part of one size and a second part of a smaller size;

a chain locker;

an anchor chain having an anchoring part of one size and a heaving part of a smaller size, said anchor chain extending from said chain locker to said anchor in the ocean floor and passing over said windlass wheel.

6. An anchoring system as defined in claim 5 including a pear-shaped connecting link between said anchoring part and said heaving part of said anchor chain.

7. An anchoring system as described in claim 5 in which a cross section through said windlass wheel defines a first T- shaped opening for said anchoring part of said chain and a second T-shaped portion for the said heaving part of said chain, the vertical part of the stem of said first T forming the crossmember of said lower T.

@ 2 2 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,5823% flnefi. 1971 lnventor(s) Don H. Fliokinger It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 3, "wellhead" should read "wellhead"; line 8, "having" should read. --heaving-.

Column 1, line 35, "of" should read -if-.

Column 3, line 36, after "small" insert -hea.ving-.

Signed and sealed this 7th day of December 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSGHALK Attesting Officer Acting Commissioner of Patents 

1. A method of mooring a ship floating on a body of water which comprises: providing a stern anchor line of two parts, a first part being of sufficient size and length to anchor said ship to a subsea anchor and a second part of a size smaller than said first part; anchoring the stern of said ship with said first part of said line; anchoring the bow of said ship; releasing the stern anchor line by lowering the first part into the water by paying out said second part sufficiently so that said stern anchor line is not effective to anchor the ship; changing the ship position as required so that it is headed into a storm; after the storm has subsided taking in on the second part of said stern anchor line to retrieve said first part; reanchoring the stern of said ship with said first part of said stern anchor line.
 2. In the method of claim 1 in which said ship is a drilling ship which includes the steps of: placing a riser pipe into the water so as to connect a subsea well with the ship, including connecting the upper end of said riser pipe to said ship; releasing said riser pipe from said well prior to releasing said stern anchor line.
 3. A method as defined in claim 2 including the step of swinging the ship about its bow so that it heads into a storm by operating the ship''s propulsion system and taking up on at least one bow anchor line.
 4. A method as defined in claim 2 in which said anchor line is a chain having an anchoring section connected to a heaving section and including the step of threading said stern anchor chain over a double sprocket system windlass having a first sprocket system being of a size to accommodate said anchoring portion, and said second sprocket system being of a size to accommodate said heaving portion; operating said windlass to take up or let out said stern anchor chain.
 5. An anchoring system for a ship floating on a body of water which comprises: an anchor; a windlass wheel for use with an anchor chain having a first part of one size and a second part of a smaller size; a chain locker; an anchor chain having an anchoring part of one size and a heaving part of a smaller size, said anchor chain extending from said chain locker to said anchor in the ocean floor and passing over said windlass wheel.
 6. An anchoring system as defined in claim 5 including a pear-shaped connecting link between said anchoring part and said heaving part of said anchor chain.
 7. An anchoring system as described in claim 5 in which a cross section through said windlass wheel defines a first T-shaped opening for said anchoring part of said chain and a second T-shaped portion for the said heaving part of said chain, the vertical part of the stem of said first T forming the crossmember of said lower T. 